31 In vitro, pharmacological inhibition of STAT5 using pimozide potentiated the effects of a JAK2 inhibitor, increasing death in HEL, SET2, and Ba/F3 JAK2V617F cells.32 Corroborating these findings, Yan et al.33 demonstrated in vivo that Stat5 is required for and plays a critical role in PV development in a murine MPN model. Here, JAK2 is linked to acquired polycythemia vera.